Topic: '75 550K1 Flat Track Build

[AlexHershey]

Hey guys....
Acquired this five fitty in a barter with my brother. I am normally a vintage Harley guy so this will just be a little back and forth to work deal while my Ironhead is down. Pretty simple for now until I decide what I need to change after riding it a bit. The bike came to me in sort of a stripped down state, no fenders or tail light, it had UNI pod filters and was missing the airbox. Luckily my brother tracked down the airbox in his room somewhere and I threw it on with a new UNI element. The bike runs halfway decent, the floats get hung up from time to time so they leak a bit. It has, from what I can tell, a Mac 4-1 with the most battered muffler I have ever seen. Ive procured some exhaust gaskets so that I can pull it off and paint it with some high temp paint and replace the muffler.

The paint is original, I just scuffed it with a gray 3M pad and took it to work and sprayed Limco clear over it. It will probably stay that way until I see fit. Does anyone have a good source for a petcock filter. Mine has the little two outlet bugger and I don't really think I can fit 2 inline filters in that amount of space.



I also messed around and fit up the back half of the rear fender and tail light off of my Ironhead and wired it up. Still searching for a half decent front fender as you can really feel the flex up front without it.


So yeah that's about it now. I'm not currently riding it as the carbs need gone through. Just been sort of rippin it around the city as I go. Been a bit busy working on this guy;

Which is currently in a million pieces awaiting a David Bird hardtail.




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[AlexHershey]

I've been looking around at everyone's 550 builds and such and can't seem to find a seat style that I like. I'm going for more of a resto-mod rather than a traditional cafe or whatever they are calling these baguette looking seats. I find the stock seat is uncomfortable as hell and feels way too wide. I don't really want to cut the subframe and I like the hinge and lock on the factory seat. Any ideas?


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[AlexHershey]

I'm capable of doing it my self, I just was looking to see what anyone has done without Welding in a hoop. The seat is definitely wider than the frame as it sort of rolls over it. Just looking to see what others have done before I really dive in.


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[RAFster122s]

The tracker brat seats are awful looking, I agree with you there. 
There is a seat how to located on the CX500 forums that is very good.  It addresses some of the ergonomics and depressions a seat should have to not put pressure on part of the male anatomy that can lead to side effects.  The different densities and shaping, etc.  It is really quite good.
He even fabricates his own cover with an industrial sewing machine.
If I recall correctly he even fitted a gel pad into the seat for more comfort.

Ostrich is a very good leather if you want to use a leather seat. A very tough and yet supple leather, albeit not cheap.

[AlexHershey]

Thanks RAF I'll have to take a look at that. Further down the line I plan to disassemble the whole mess and build a little hooligan flat track bike but for no w I'd like to be able to ride it without feeling like I'm on a Clydesdale.

Calj, I see what you are saying. The hinges keep it from being totally flush with the rails.


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[AlexHershey]

Change of direction, this thing is being built to go fast(ish) in the dirt! Will be stripped of everything making it road legal and built to run AMA Vintage events. Piston Poppers TT track is 1 mile from where I work and I am looking forward to hopefully running there at least once this season and then hopefully branch out to the rest of District 6 next season. Any comments from experienced flat trackers here will be greatly appreciated. I know it is not the best bike to start with, I am not looking to be the top dog. My grandfather ran these tracks in the 60's and 70's on whatever he could afford at the time so I plan to make use of what I already have. It will get as light as I can make it safely, and I think with proper gearing it could be at least mid pack (user error not taken into account. Haha)


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[AlexHershey]

If by any chance a Moderator could change the title to '75 550K Flat Track Build that would be cool.


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[SOHC4 Cafe Racer Fan]

Also twins and singles tend lend themselves better to flat trackers as opposed to in-line fours, for power delivery.  Take a look at the field of flat track bikes for the last 40 years and the engines they run.  This is because certain twins and singles "hook up" better than inline fours on a dirt track.  Honda's old flat trackers were twins, too.  Check out the RS750.

This year, all factory teams are racing water-cooled twins.  The air-cooled Harley-Davidson XR750 is now relegated to privateers.

As for sohc4 engines, the 550 engine is likely better than a 750, as the 550 engine (I believe) has a lower COG, or just less mass up high.  That said, if this is really a "street tracker" -- street bike inspired by flat track, you can definitely bring that aesthetic to a CB550.

If you really want to race dirt flat track, you might want to start with a different platform than a CB550.  Just saying . .  .

[AlexHershey]

I am well aware of all of those point, as I have been following the sport for some time. While I ultimately lust after an xr750 or an early 900cc sportster to rip around, the wallet does not agree. It's vintage racing, so while competitive, it's not Nationals level racing. I'm looking for the most smiles for the least amount invested. I have the CB already, and am in it for $0. Parts are inexpensive as opposed to some other manufacturers. It does have a half decent amount of low /midrange torque and will be sorted better with gearing selection. With more seat time I hope to acquire a more Suitable bike. But for now, the CB will do.


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[AlexHershey]

Nothing wrong with the nature of the motor, its the frame and suspension that will kill you (price wise). But the motor is heavier than ideal. Can be done, but you need to give due thought to the suspension modifications so the bike handles decently and doesn't high side you when it catches  on the low side in a turn. Know what I mean?

Absolutely. That is my main concern. I'm not all that worried about making more power or any other fancy bits. I have been researching suspension and will be doing so further to find the best solution. In reality, it will never hang with the 500+cc twins, but it is more or less an exercise in how far I can develop this bike as my initial cost is nil. I do have a fellow interested in trading a cb360 for it, but I fear that may be going in the opposite direction.


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[AlexHershey]

If you could find a 450 twin, or even a 350 twin, you would have a really fun platform. There's a member selling 2 very nicely done up 350s, but you'd be heavily invested. 

Right that would be ideal. I'm going to probably still check this 360 out and see if it's something that interests me. It would definitely be lighter (barely) and put me in a better class so that at least is a plus.


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[SOHC4 Cafe Racer Fan]

If you could find a 450 twin, or even a 350 twin, you would have a really fun platform. There's a member selling 2 very nicely done up 350s, but you'd be heavily invested. 

Right that would be ideal. I'm going to probably still check this 360 out and see if it's something that interests me. It would definitely be lighter (barely) and put me in a better class so that at least is a plus.


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The 360 was geared mostly for mileage and are similar but not interchangeable with the 350 twins.  The 350 twins have loads of aftermarket go-fast parts available. 

[AlexHershey]

I agree that the 360 doesn't have quite the same aftermarket and in stock form are more on the docile side but I think that it is definitely a viable option.


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[754]

How big is the track ? My 750 sucked on the dirt . 350 XL much better..here is a 74 I sold in January ...makeover is near finished..weighs about 230 lbs
 It is now painted and has exhaust on it..

[AlexHershey]

Piston Poppers is a ¼ track. I do agree that a sub 350cc bike is ideal. I have put the 550 up for sale in the area and basically got no serious interest so unless the trade for the 360 works out I am working with the 550. Again, I'm really not terribly obsessed with being fast, or even competitive. This is purely a fun venture. I would love to unload the 550 and buy something more suited but it just hasn't happened, so here I am. 


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[AlexHershey]

Yup located in Central PA. Lancaster to be exact. There are a ton of big name flat track people around here I just am not plugged in to that circle...any help is much appreciated.


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[SOHC4 Cafe Racer Fan]

My buddy converted an XL250R to a flat track bike withe a modern front.  He paid $200 for the donor.  He would swap the wheels/tires as he road it on street and track.

https://www.lossaengineering.com/blogs/bikes/36816707-honda-xl250r-flat-tacker

[AlexHershey]

Ah yeah that is a killer ride. Jay has a cool style.


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